1. Technical Field
The present invention relates to integrated circuit devices having improved backside probing capability. More particularly, the present invention relates to the use of deep trenches which have been critically fabricated with respect to degree of depth and location to facilitate characterization, diagnostic testing, and potential defect detection during development, manufacture, and usage. The conductive portions of the trenches can be accessed by conventional electrical probing methods after the backside of the semiconductor chip has been subjected to standard polishing techniques, followed by milling with focused ion beam, laser-assisted etch techniques, or chemical etching.
2. Background Art
In the manufacture of semiconductor devices, the ability to obtain waveform measurements from internal nodes has been found to be critical to carryout failure analysis and characterization. Often active surfaces of the semiconductor devices are obscured by I/O(input/output) circuits, interconnect wiring, packaging, or limitations of the probing apparatus.
During the integrated circuit development phase, early engineering hardware is often characterized by subjecting the device to various test conditions such as speed, temperature, etc. Measuring and diagnosing the performance of these devices is done by acquiring waveforms from key circuit nodes within the device such as clock lines, enable signals, address buses, and data buses. If the early engineering hardware does not perform adequately, or is non-functional, it is critical to be able to trace back signals to the source of the problem. A convenient mode of detecting such failure source is by waveform analysis. The ability to diagnose problems by waveform analysis is also necessary during manufacture and throughout the life of the product so that corrective action can be taken.
Those skilled in the art know that waveforms can be acquired from internal circuit nodes by direct-contact mechanical probing or electron-beam probing. Additional techniques such as laser-induced light also have been reported. In order to prepare a device for diagnosis, it is necessary to establish electrical contact with a tester and one or more of the numerous Input/Output (I/O) circuits in the device. In some instances, these I/O circuits are placed in the periphery of the device, or located in a manner to provide some degree of access to the device""s active surface by some form of mechanical or electron beam probe during operation. However, as a result of increasing circuit complexity, a trend toward higher density packaging, or the density of the I/O circuits and related probes needed to activate the device, improvments in semiconductor device structures to provide enhanced means for mechanical or electron beam probe are needed.
To facilitate electrical access to the I/O of the IC, additional circuits and pads are frequently positioned adjacent to, or on the upper-most level of the IC die. Quite frequently, such IC dies with I/O circuit elements situated on the top surface have the disadvantage of obstructing internal circuitry. Additionally, packaging methods, often referred to as a xe2x80x9cflip-chipxe2x80x9d, xe2x80x9cC4xe2x80x9d, or direct chip attach (DCA), can be attached upside-down, or flipped onto a package substrate, or directly onto a circuit board, flexible cable, or other assembly into which the IC is interconnected. As a result, the internal circuit nodes of the IC are buried and inaccessible for characterizing electrical circuit performance, performing diagnostic testing, or performing failure analysis while the IC is operating normally and in a fully functioning state.
A procedure for monitoring the fabrication of a semiconductor device using an electrical characteristic such as resistance is shown by Rostoker, U.S. Pat. No. 5,321,304. A semiconductor wafer is provided having vias through the wafer, and a contact structure at the top to provide a conductive path through the wafer. An insulating layer overlies the contact structure to signal the endpoint of chem-mech polishing. Lu et al, U.S. Pat. No. 4,688,063, incorporated herein by reference, shows the feasibility of introducing a storage capacitor in a semiconductor device in the form of a trench capacitor which is used as part of a Dynamic Random Access Memory (DRAM) cell. The trench capacitors are positioned from the surface of semiconductor device to a heavily doped region within the cell. A DRAM cell is shown which uses a field effect transistor (FET) and a trench capacitor which forms a well in the semiconductor substrate. An electrode disposed in the trench capacitor is directly connected to the source drain of the access transistor.
While exterior conductive contact structures connected to vias extending through a semiconductor wafer have been used to facilitate the polishing of such wafer, or trench capacitors have been disposed in a semiconductor substrate as part of a DRAM cell, nothing is shown by the art to satisfy the need for enhanced characterization, diagnosis, or failure analysis capability in semiconductor devices through mechanical or electron beam probe techniques, particularly from the backside of the die.
It is an aspect of the present invention therefore to provide a system for obtaining access to internal circuit nodes of fully processed and packaged integrated circuits (IC""s) for the purpose of making electrical measurements to facilitate electrical characterization, diagnostic testing, and failure analysis.
It is another aspect of the present invention to provide test points which can be incorporated into the design of an IC without adversly affecting the operation of the device.
It is a further aspect of the present invention to provide internal IC test points which can be readily accessed for electrical characterization, diagnostic testing, and failure analysis.
It is an additional aspect of the present invention to provide a method for accessing internal test points through the back or reverse-side of an IC in a non-invasive manner.
Accordingly, the present invention is directed to the use of trenches in a semiconductor device which have been fabricated in preselected locations. The trenches are filled with a conductive material and are electrically connected to particular circuit nodes of the semiconductor device to provide readily accessible test points which are also suitable for backside electrical probing. Unlike a trench capacitor normally used as a memory cell in a semiconductor device, trenches used in the integrated circuit devices of the present invention are insulated on the sidewall to the extent that their performance as capacitors is substantially precluded.
There is provided by the present invention, an integrated circuit comprising a plurality of interconnected circuits, each having a plurality of internal circuit nodes, and at least one circuit node accessing means including an insulated electrical conductor extending from a surface of the integrated circuit to a point substantially below the surface and positioned to facilitate non-invasive electrical probing of at least one preselected circuit node via the backside of the substrate.